Prominent seasonality of 25(OH)D vitamin deficiency in Latvia: Age and gender-related variations and testing regimen

Abstract

Seasonality of 25(OH)D deficiency rate is a factor of major clinical and social impact and should be considered when planning for appropriate testing and tailored correction. We present retrospective cross-sectional analysis of over a million 25(OH)D tests performed in two leading Latvian laboratories – Central Laboratory and E.Gulbja Laboratory. Both series of tests demonstrated prominent seasonal variability of 25(OH)D deficiency rate (<20 ng/ml) and critical deficiency rate (<12 ng/ml): the lowest percentage of deficient tests was in August, while a significant peak was found in March-April. This trend was present at all ages and in both genders, variations were pronounced even for a high-latitude country and more prominent for critical deficiency, in younger age groups and in males. Analysis of testing regimens of both laboratories revealed that schedule was not optimal, period of higher testing intensity being far removed from the 25(OH)D deficiency peak.